A person’s “memory” is the stored form of all types of acquired personal knowledge, including both knowledge of personal experiences (episodic memory) and knowledge of patterns perceived in the world (semantic memory), such as the knowledge that staying safe around one’s rage-prone, alcoholic parent urgently requires never expressing any views or feelings of one’s own. This article explores the possibility of (a) understanding most, if not all, psychotherapeutic action as a reconfiguration of knowledge held in memory and (b) identifying each of the distinct, fundamentally different endogenous mechanisms, or types of processes, that can modify memory therapeutically. In this way, a potential means of unifying psychotherapy emerges, enabling us to identify how any particular therapeutic process influences symptom production through its memory modification effects. Memory neuroscience has identified mechanisms of memory modification sufficiently for the proposed explorations to be pursued fruitfully at this point. The resulting unification scheme consists of two qualitatively different, main modes of memory modification, each with submodes. This scheme can account for the full range of therapeutic outcomes, from partial, unstable, relapse-prone symptom reduction to transformational change, defined here as the enduring cessation of a symptom and its underlying theme of emotional distress. Case vignettes illustrate the fundamental modes and some submodes of therapeutic memory modification. Viewed through this unification framework, diverse therapy systems no longer seem to belong to different worlds. Rather, their distinctive techniques and methodologies become a rich array of options for tailoring memory modification and therapeutic change uniquely for each person.